Graduate School of Sport and Health Science, Ritsumeikan University , Japan.

Abstract

Influence of different load exercise to muscle activity during subsequent exercise with 75% of one repetition maximum (RM) load among trained and untrained individuals was verified. Resistance-trained men who were involved in resistance training (n = 16) and healthy young men who did not exercise regularly (n = 16) were recruited for this study. Each subject performed bench pressing with a narrow grip exercise using two different training set methods, the drop-set (DS) (3 sets × 2-10 repetitions with 95-75% of 1RM) and the reverse drop-set (RDS) (3 sets × 3-10 repetitions with 55-75% of 1RM). The mean concentric contraction power, root mean square (RMS) of electromyography (EMG), area under the oxygenated hemoglobin (Oxy-Hb) curve, and time constant for muscle oxygen consumption (TcVO2mus) values of the triceps brachii were measured during and after the DS and RDS. The trained group demonstrated significantly higher mean muscle power (242.9 ± 39.6 W vs. 215.8 ± 31.7 W), RMS of EMG (86.4 ± 10.4 % vs. 68.3 ± 9.6 %), and area under the Oxy-Hb curve (38.6 ± 7.4 %• sec vs. 29.3 ± 5.8 %• sec) values during the DS than during the RDS (p < 0.05). However, in the untrained group none of the parameters differed significantly for both the DS and RDS. Furthermore, a negative correlation was detected between the area under the Oxy-Hb curve and muscle thickness (r = -0.51, p < 0.01). Long-term effects of DS on muscle strengthening and hypertrophy will be explored in further research.

An example of the changes in Oxy-Hb levels detected by NIRS. The Oxy-Hb level recorded at rest was defined as 100%, and the minimum Oxy-Hb plateau level recorded after 6 minutes’ arterial occlusion was defined as 0%. Furthermore, repeated arterial occlusion was performed after the exercise, and the time it took for the oxygen consumption rate to return to 63% of its resting value was calculated.

Mean muscle power of triceps brachii muscle during concentric contractions using a load of 75% of the subject’s 1RM in the trained and untrained groups during the drop-set (DS) and reverse drop-set (RDS) methods. Means ± SD (n = 16 for each group) values are shown. * Significant difference (p <0.05)

Typical example of an area under the Oxy-Hb curve. The Oxy-Hb level observed at rest was defined 100%, and the minimum Oxy-Hb plateau level induced by arterial occlusion was defined as 0%. The mean Oxy-Hb level was calculated every five seconds during exercise. The area under the Oxy-Hb curve was obtained from the product of the time (sec) and the mean Oxy-Hb (%). The gray regions represent the area under the Oxy-Hb curve.

Area under the Oxy-Hb curve values of the trained and untrained groups during the drop-set (DS) and reverse drop-set (RDS) methods. Mean ± SD (n = 16 for each group) values are shown. *Significant difference (p <0.05)